Not at all normal. All cabinet box components should be built from prefinished sheet goods. The boxes are either prefinished blanks, or finished in the spray room. As should all of the doors and drawers. If you’re getting finished in place anything, you need to put this on pause.

Well. I think definitive and hard answers like live_oak gives can be misleading, because that goes to a production norm used in most applications where builds are done in a factory.

If you are building a full custom kitchen, with a cabinetmaker who is hand-making each piece, then unfinished wood is a correct standard, the same that is used in furniture-making. Without photos of what you are building, or more details, its difficult to say.

Your preference is for a spray-sealed interior, so talk to your guy about that and see what he says. Sealing can be done with shellac (not water-resistant) or lacquer, or leave them bare and let them age naturally. If I were building full custom cabinets in my own home, my preference would be to leave them bare on the interiors.

I just looked at our vanity cabinet: unfinished. Kitchen cabinets are finished. Old furniture is unfinished. So I don't think there's a hard and fast rule.

Any materials that are placed in a kitchen should be finished prior to placement. Even local custom cabinet makers finish their goods properly before install!

A couple coats of a wipe-on finish is fine for drawer boxes.